1. Field of the Invention
The present invention relates to a combustion chamber for internal combustion engines and more specially to an inner wall surface shape of the combustion chamber.
2. Description of the Prior Art
In order to allow intake air and combustion gas to smoothly flow into or from a combustion chamber for an internal combustion engine, the shape of the inner wall surface of the combustion chamber is important. With a view to improving the charging efficiency, the same applicant has already proposed a combustion chamber for an internal combustion engine in Japanese Published Examined (Kokoku) Utility Model Application No. 51-21203. In this prior-art combustion chamber, as shown in FIG. 1A, an end surface 131 of a valve seat onto which an intake valve 130 is seated and an inner wall surface 132 on the cylinder head side are connected smoothly through a continuous spherical surface, so that whenever the intake valve 130 is opened, intake air can smoothly flow along the valve seat end surface 131 and then the spherical inner wall surface 132 under a low flow resistance.
In the prior-art combustion chamber shown in FIG. 1A, however, there still exists a problem in that vortexes are easily produced along the inner wall surface of the combustion chamber on the cylinder head side as shown in FIGS. 1B and 1C, and therefore the charging efficiency drops. The reason is as follows: when the inner wall surface 132 is formed so as to be curved by a small radius R1 in contact with the valve seat end surface 131, an angle .theta. subtended by a tangent line A on the inner wall surface and the central line O.sub.130 of the intake valve 130 decreases as the tangent line A moves from that A1 (.theta..sub.1) near the valve seat end surface 131 to that A2 (.theta..sub.2) remote from the same end surface 131, as shown in FIG. 1B, so that vortices are produced due to contraction or compression at positions remote from the valve seat end surface 131.
On the other hand, when the inner wall surface 132 is formed so as to be curved by a large radius R2 larger than R1, an angle .theta. subtended by a tangent line A on the inner wall surface and the central line O.sub.130 of the intake valve 130 increases as the tangent line A moves from that A1 (.theta..sub.1) near the valve seat end surface 131 to that A3 (.theta..sub.3) remote from the same end surface 131, as shown in FIG. 1C, so that vortices are produced due to separation or expansion at positions remote from the valve seat end surface 131.